In porous mortar or porous concrete, according to the type of production method, a distinction is made between cellular concrete or cellular mortar and foamed concrete or foamed mortar. Cellular concrete is only produced in special concrete constructions and contains an expanding agent made of highly explosive hydrogen, which is generated by reaction of aluminum with cement in the concrete and which forms pores. This method requires a complex process controlling and is very energetic, and cannot be performed on site or at construction sites.
In foamed concrete or foamed mortar, a harmless foam is used as a pore-forming agent. This method requires a foaming agent, a foam generator, a foamed concrete mixer as well as a pump. The foam produced with the foam generator and the foaming agent is directly admixed with the finished mixed concrete or mortar. This method can be easily controlled, is energy-saving, time-saving and is suitable for mobile use. It allows a reduction of density of concrete or mortar from 1900 kg/m3 up to 400 kg/m3. A decisive drawback of “pre-foaming” consists in that it is almost impossible to mix the finished foam in a uniformly dosed manner, whereby deviations within the finished mixture in excess of 20% are caused. The drying time in this method lies between about 4 and 8 days.
The foaming agents are defined, according to active agent base, as protein-based and surfactant-based (synthetic foaming agents).
Protein-based foaming agents are usually produced by protein-hydrolysis of animal proteins, from horn, blood, bones and similar wastes of cattle, pigs and other animal cadavers. Varying raw materials cause fluctuations in the end product as well as a very unpleasant smell of products.
Synthetic foaming agents are of purely chemical origin at constant quality, and are used for producing foamed concrete, but are not preferred, due to their frequent lower stability.
In general, a drawback of pre-foamed foam lies in the fact that no 100% mixing with the binder cement or plaster is possible.